Surface-mount technology

Surface-mount technology is a method in which the components are mounted or placed directly onto the surface of a printed circuit board. An electronic device so made is called a surface-mount device. In industry, it has replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board. Both technologies can be used on the same board, with the through-hole technology used for components not suitable for surface mounting such as large transformers and heat-sinked power semiconductors. By employing SMT, the production process speeds up, but the risk of defects increases due to component miniaturization and to the denser packing of boards. In those conditions, detection of failures has become critical for any SMT manufacturing process. An SMT component is smaller than its through-hole counterpart because it has either smaller leads or no leads at all, it may have short pins or leads of various styles, flat contacts, a matrix of solder balls, or terminations on the body of the component.

Surface mounting was called "planar mounting". Surface-mount technology was developed in the 1960s and became used in the mid 1980s. By the late 1990s, the great majority of high-tech electronic printed circuit assemblies were dominated by surface mount devices. Much of the pioneering work in this technology was done by IBM; the design approach first demonstrated by IBM in 1960 in a small-scale computer was applied in the Launch Vehicle Digital Computer used in the Instrument Unit that guided all Saturn IB and Saturn V vehicles. Components were mechanically redesigned to have small metal tabs or end caps that could be directly soldered to the surface of the PCB. Components became much smaller and component placement on both sides of a board became far more common with surface mounting than through-hole mounting, allowing much higher circuit densities and smaller circuit boards and, in turn, machines or subassemblies containing the boards. Only the solder joints hold the parts to the board. Adhesive is sometimes used to hold SMT components on the bottom side of a board if a wave soldering process is used to solder both SMT and through-hole components simultaneously.

Alternatively, SMT and through-hole components can be soldered on the same side of a board without adhesive if the SMT parts are first reflow-soldered a selective solder mask is used to prevent the solder holding those parts in place from reflowing and the parts floating away during wave soldering. Surface mounting lends itself well to a high degree of automation, reducing labor cost and increasing production rates. Conversely, SMT does not lend itself well to manual or low-automation fabrication, more economical and faster for one-off prototyping and small-scale production, this is one reason why many through-hole components are still manufactured; some SMDs can be soldered with a temperature-controlled manual soldering iron, but those that are small or have too fine a lead pitch are impossible to manually solder without expensive hot-air solder reflow equipment. SMDs can be one-quarter to one-tenth the size and weight, one-half to one-quarter the cost of equivalent through-hole parts, but on the other hand, the costs of a certain SMT part and of an equivalent through-hole part may be quite similar, though is the SMT part more expensive.

Different terms describe the components and machines used in manufacturing. These terms are listed in the following table: Where components are to be placed, the printed circuit board has flat tin-lead, silver, or gold plated copper pads without holes, called solder pads. Solder paste, a sticky mixture of flux and tiny solder particles, is first applied to all the solder pads with a stainless steel or nickel stencil using a screen printing process, it can be applied by a jet-printing mechanism, similar to an inkjet printer. After pasting, the boards proceed to the pick-and-place machines, where they are placed on a conveyor belt; the components to be placed on the boards are delivered to the production line in either paper/plastic tapes wound on reels or plastic tubes. Some large integrated circuits are delivered in static-free trays. Numerical control pick-and-place machines remove the parts from the tapes, tubes or trays and place them on the PCB; the boards are conveyed into the reflow soldering oven.

They first enter a pre-heat zone, where the temperature of the board and all the components is uniformly raised. The boards enter a zone where the temperature is high enough to melt the solder particles in the solder paste, bonding the component leads to the pads on the circuit board; the surface tension of the molten solder helps keep the components in place, if the solder pad geometries are designed, surface tension automatically aligns the components on their pads. There are a number of techniques for reflowing solder. One is to use infrared lamps. Another is to use a hot gas convection. Another technology, becoming popular again is special fluorocarbon liquids with high boiling points which use a method called vapor phase reflow. Due to environmental concerns, this method was falling out of favor until lead-free legislation was introduced which requires tighter controls on soldering. At the end of 2008, convection soldering was the most popular reflow technology using either standard air or nitrogen gas.

Each method has its disadvantages. With infrared reflow, the board design

Musaeus College

Musaeus College is a private girls' school in Colombo, Sri Lanka. The school is named after its founding principal, Marie Musaeus Higgins from Wismar, who served as the school's principal from 1891 to 1926. Musaeus College provides primary and secondary education to more than 6,700 girls from ages 3 to 18, is managed by a board of trustees; the school's motto is "Follow the Light". The origin of the school can be traced to the Women's Education Society of Ceylon, whose mission was to improve educational opportunities for girls, with instruction in English along with Buddhist principles, it had the backing of the Buddhist Theosophical Society, which founded the Ananda College for boys along similar lines. With help and guidance from Peter De Abrew and Colonel Henry Steel Olcott, they founded the Sangamitta Girls' School at Tichborne Place, around 1890, wanted a European lady as its Principal. Colonel Olcott found a suitable candidate in Kate F. Pickett, the daughter of Elise Pickett, President of the Melbourne Theosophical Society.

Miss Pickett arrived in Colombo on 10 June 1891 and had settled into life in the school's boarding house when she was found on the morning of 24 June 1891 drowned in a well in the school grounds. Marie Musaeus Higgins, after whom the College was subsequently named, was the daughter of Theodor Musaeus, Chief Justice of Wismar in Mecklenburg, Germany. After having graduated and obtaining the title of Frau Professor, she proceeded to the United States of America and was engaged in educational work there, she married an engineer in the US army and a Theosophist. He died less than four years later. Following an advertisement by Col. Olcott in The Path, she left for Ceylon, arriving on 15 November 1891; the Musaeus Buddhist Girls' School started in a simple and modest ‘mud hut’ which served both as living and teaching quarters with 12 students. The ‘hut’ was replaced by a brick building in the year 1895 as a result of a donation from Mr. Wilton Hack, he was a recent convert to Theosophy and around 1892, while in Colombo on his way home to Australia, Hack observed the work being carried out by Higgins, decided to become involved in its development.

He was to remain on the board of trustees until his death in 1923. The lack of sufficient classrooms had stood in the way of Government assistance. Whenever Higgins had approached Mr. J. B. Cull, Director of Public Instruction, for funds she was told that without a permanent building she was ineligible for a Grant. Once the fine new hall with its upper storey to serve as a teaching hall and extra dormitory was completed, an annual Government grant to the school followed. Teachers’ Training School The demand for women teachers for Sinhalese Buddhist Girls’ schools being great, Higgins was approached by the Manager of those schools to open a Training College to train women students as school teachers; this work was begun in 1908 with the sanction of the Government. This College was now sending out annually a number of trained teachers as Head-Mistresses of Buddhist Sinhalese Girls’ Schools, situated out of Colombo. There was a Practicing School attached to the Training College. Not only did it form and indispensable adjunct to the College, but the mean of giving a free education in Sinhalese to the children in the neighborhood.

The work of the Musaeus Buddhist Girls’ College was thus confined to:- English College Kindergarten on Modern Lines Training College for women Practising School Works on Buddhism Higgins’ historical studies induced her to study Buddhism and in her years Higgins was engaged in the task of compiling books on Buddhism “Poya Days” and “Jataka Mala” are two of her popular books. Higgins had planned to issue a series of plays called “Ceylon Historical Plays”, she published one or two of them and they were acted out under her own supervision by the girls of Musaeus College. Her simplicity of style had a special appeal to children for; as a social religious worker, Higgins was held in high esteem. Her life was devoted to the cause, which she represented. In years, she was not in the best of health-due to a life of strenuous hard work; the climate of Colombo did not agree with her and during the greater part of the year she lived at “Musaeus Cottage”, Diyatalawa. She was compelled to give up the Principalship of the school and become the Director.

During the last few days Higgins was ill. She had more than one relapse and her condition continued to give anxiety. At the time of her death, her niece, Miss. Schneider who arrived from Germany, was looking after her, was by her bedside when she died at the age of 71. At a time when Western influences were becoming widespread, Higgins encouraged her students to uphold their traditional customs and culture, she made religious activities an integral part of the school curriculum. After 33 years of service Higgins died in 1926. ‘Founder-Father’ of Musaeus Peter De Abrew was the eldest son of William de Abrew. He was one of the pioneers of the Theosophical Society of Ceylon. De Abrew became involved in the movement started by Colonel Henry Olcott and others towards the regeneration of the Sinhala nation, its religion and culture which had deteriorated during the last decades of the 19th Century together with his father, William de Abrew, himself a member of this movement donated their own land to build a Buddhist Girls’ School.

Higgins and de Abrew started their school in 1891, in a little thatched mud-walled hut where Musaeus stands now. In 1940 Peter De Abrew died at the age of 78. Motto: The schoo


Ectodysplasin-A receptor-associated adapter protein is a protein that in humans is encoded by the EDARADD gene. This gene was identified by its association with ectodermal dysplasia,and with hypohidrotic ectodermal dysplasia, a genetic disorder characterized by defective development of hair and eccrine sweat glands; the protein encoded by this gene is a death domain-containing protein, is found to interact with EDAR, a death domain receptor known to be required for the development of hair and other ectodermal derivatives. This protein and EDAR are coexpressed in epithelial cells during the formation of hair follicles and teeth. Through its interaction with EDAR, this protein acts as an adaptor, links the receptor to downstream signaling pathways. Two alternatively spliced transcript variants of this gene encoding distinct isoforms have been reported. EDARADD has been shown to interact with TRAF2. GeneReview/NIH/UW entry on Hypohidrotic Ectodermal Dysplasia